The Guardian's investigation, published on Monday, into the death rates in vascular surgery in the NHS was underpinned by rigorous statistical analysis.

We collected data from 116 hospital Trusts using Freedom of Information requests - asking not for the hospital's administrative data, known as HES (hospital episode statistics) but the surgeons' own information on mortality rates within 30 days of surgery - in elective (planned) operations for abdominal aortic aneurysm, or AAA, surgery and in ruptures.

We shared the data, which took 18 months to collect, with the country's top experts in the analysis of outcomes from vascular surgery.

Today, in response to those who have asked to see them, we are publishing the graphs drawn up by Peter Holt, clinical lecturer in vascular surgery at the department of outcomes research of the Vascular Institute at St George's Healthcare NHS Trust. They show very variable mortality rates around the country for elective and rupture surgery and they also show a relationship between volume and outcome - the more AAA cases a hospital does, the better its results are likely to be. This is a link to Holt's paper on the safety chart.

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The data we collected on surgeons' AAA mortality rates between 2006 and 2008 was analysed for the Guardian by Peter Holt, clinical lecturer in vascular surgery in the department of outcomes research at the Vascular Institute of St George's Healthcare NHS Trust In London. These are his graphs and safety plots.